The present invention relates generally to power tools, and more particularly provides a substantially improved power head assembly, and vibration reducing apparatus, for a portable rotary power tool such as a flexible line trimmer.
Portable, gasoline engine driven rotary power tools such as brush cutters, lawn edgers, flexible line trimmers and the like typically comprise an elongated hollow shaft to one end of which a rotary cutting assembly is operatively mounted. A power head assembly, including the engine, is mounted on the opposite end of the shaft and typically comprises a protective shroud structure which envelops all or part of the engine, a gas tank, and a recoil starting mechanism incorporating the usual starter rope and pull handle components. The engine drives the cutting assembly, either directly or through a clutch mechanism, via a flexible drive shaft structure extending through the hollow shaft. To assist in properly guiding the cutting element during tool use, a pair of operator handle elements are typically secured to the tool in appropriate locations thereon. Additionally, a shoulder strap is often used to support the weight of the tool, the strap having an outer end portion which is releasably connectable to a small rigid clamp member or the like secured to the shaft.
While gasoline driven tools of this general type and configuration have proven to be quite useful, and immensely popular, a variety of problems, limitations and disadvantages may still be found in many of them relating to, among other things, structure, operation, safety, fabrication cost effectiveness, operating comfort, and maintenance and service accessability.
For example, because of the need to design the power head assembly to be at the same time light in weight, compact, and cost effective from material and fabrication standpoint, the resulting power head assembly can be frustratingly difficult and laborious for the average consumer to work on. Even minor engine adjustments, such as resetting the carburetor idle and operating speed adjustment screws, is often annoyingly hindered by the need to disassemble and remove various other power head components to even reach the carburetor. At the other end of the maintenance spectrum, major engine teardown and removal is often simply beyond the capabilities of the average tool user due to the sheer complexity and intricacy with which many conventional power heads of this general type are of necessity assembled.
Conventional attempts to alleviate to some degree this component access problem have, in many instances, left certain engine components exposed in a manner, though increasing their accessability, increasing the likelihood that such exposed components will be accidentally bumped and damaged during tool use, and giving the overall power head a somewhat ungainly and "jury rigged" exterior appearance. As but one example of this problem, the engine's carburetor and associated air filter structure are often allowed to protrude outwardly of the engine's shroud structure for accessability purposes, thereby rendering these components highly vulnerable to damage.
Another example, relating both the component accessability and safety, arises in conjunction with the recoil starter mechanism which is typically difficult to remove and, when the need arises to replace its starter rope, difficult, awkward and sometimes unsafe to work on. As is well known, the problem here lies with the conventional necessity of hand winding the starter pulley against the biasing force of its associated torsion spring, and then holding the wound-up pulley with one hand, to keep the torsion spring from flying off, while attempting to rethread and knot a new starter rope onto the pulley with the other hand.
Apart from these and numerous other problems typically associated with conventional power head sections of tools of this general type, it has been found that a surprisingly high amount of shaft vibration is often transmitted to the tool operator's body through the shoulder strap secured to the tool shaft despite the flexibility of the strap. This transmitted vibration can be both annoying and tiring, and it would be quite desirable to eliminate or at least substantially reduce it in a simple, inexpensive manner.
In view of the foregoing, it is accordingly an object of the present invention to provide improvements which eliminate or minimize above-mentioned and other problems, limitations and disadvantages commonly associated with conventional portable rotary power tools of this general type.